The invention relates to an apparatus for producing cement clinker from wet slurry raw materials that are mechanically dewatered, dried, heated in a cyclone suspension type heat exchanger system, calcined in a calcining step, calcined to cement clinker in a rotary furnace and cooled in a clinker cooler.
A known method of the cement clinker manufacture, the wet method, is characterized in that the utilized wet raw materials are milled together in wet-process rotary tubular mills in order to thus receive a fine grained and intimately mixed raw slurry. Then, this raw slurry is directly calcined to clinker in a wet-process tubular furnace, potentially with chain inserts, or is formed to pellets after a preliminary desiccation, which pellets are subsequently calcined in the rotary tubular furnace.
In the course of time, the drying method, which is thermally more beneficial, has succeeded, whereby raw materials that are milled in a dry fashion are calcined to cement clinker in a rotary tubular furnace with a preceding cyclone suspension type heat exchanger system.
Given the conversion of present wet apparatuses into modern drying apparatuses, it is known to maintain the wet-processing of the raw material and to convert the slurry raw material (raw meal slurry), by means of a mechanical and subsequent thermal dewatering, into a dryness required for feeding the cyclone heat exchanger.
For example, it is known to bring the raw slurry from the wet-grinding mills from its pumpable moisture up to a moisture of approximately 20% via a mechanical dewatering in the form of filter presses, drum filters etc. Then, the received filter cake is thermally dried, with respect to the required residual moisture of preferably 0.5 through 1.0%, in a flight stream drier, for example, which comprises an impact hammer breaker, a rising tube and a separator. Further, it is known to carry out the thermal drying in a drum type drier or in flash driers with throwshovels or in impact driers.
The industrial outlay required for the drying of the filter cake by means of utilizing rotating machine parts is disadvantageous with respect to the cited drying apparatuses, which are actually designed for the mill drying. For example, the impact hammer breaker of the flight stream drier must be dimensioned regarding its power draw such that the hammers are pulled through the material, which is still moist, at the impact hammer breaker bottom even when the drying power is not sufficient.
EP-B-0 650 763 discloses a circulation crushing plant with a high-pressure roller press for the interparticle comminution of the material to be fed and with a static cascade separator that works according to the principle of a cross current separator, which can be operated by means of air and also by means of hot gas when the feed to be crushed is moist, so that the crushing plant is then utilized for the mill drying. It is not known to utilize such a circulation crushing plant or parts thereof with respect to the what is referred to as wetprocess for purposes of manufacturing cement clinker from wet slurry raw materials.
The invention is based on the object of fashioning the thermal drying of the filter cake in terms of the apparatus such that the drying is adapted to the specific properties of the fine grained filter cake and to the objective of the drying of the manufacture of a raw meal that is appropriate for feeding the cyclone suspension type heat exchanger system, whereby the construction and cost outlay is low given the manufacture of cement clinker from wet slurry raw materials.
As a result of the inventionxe2x80x94which dries the fine grained filter cakes that arise during the mechanical preliminary dessication in a static step drier, which is pressurized with hot gas of approximately 340xc2x0 C. through 550xc2x0 C. from the cyclone suspension type heat exchanger system of the rotary tubular furnace, up to a residual moisture of 0.5 through 1.0.%xe2x80x94a raw meal, which is suitable for feeding the cyclone heat exchanger, is produced with simple means concerning the construction and with low operating expenses.
The step drier is equipped with two separating and drying zone limiting walls, which are surrounded by the shaft-shaped housing and which form a separating zone and drying zone between them and which are traversed by hot gas in a cross current, which separating and drying zone limiting walls have baffles that are transversely downwardly slanted in the direction of the discharge opening for separated coarse material that is possibly still moist and that are arranged in a cascade-like manner which could include being slatted, whereby the two baffle walls and therefore the separating and drying zone lying therebetween are obliquely arranged with an angle deviating from the vertical line.
The hot gas that is required for the drying is tapped, with temperatures of approximately 340xc2x0 C. through 550xc2x0 C., at a suitable location from the cyclone heat exchangers of the rotary tubular furnace; this is the reason why the step drier is also designed for these temperatures. The hot gas is laterally introduced into the step drier via a corresponding opening; it initially passes the separating and drying zone of the step drier in the cross current and then leaves the step drier on the other side of the drying zone, for example via an upper opening, and is now loaded with dried raw meal.
The drying in the step drier ensues as follows. The filter cake from the mechanical dewatering, particularly filter press, is supplied via a filter cake conveying device to the admission opening, which is arranged in the upper part of the step drier and which is provided with a mechanical milling device, such as a hasp and is coarsely crushed there. Then, the filter cake pieces arrive at the separating and drying zone of the step drier and come in contact with the hot gas. Due to the suddenly arising vaporization, the filter cake pieces are spread out in all directions and are therefore crushed further. The crushed material, with gravitational force, falls downward via the steps of the step drier, which steps are fashioned in the shape of cascades, and is thereby dried further by means of the hot gas. The thereby received dried fine material-raw meal with a residual moisture of, for example, 0.5 through 1.0% is laterally or, respectively, upwardly outlet in the step drier together with the hot gas and the formed vapors, and is then transported out of the step drier at the upper end of it. In a cyclone pre-separator that follows the step drier, the dried fine material is separated from the hot gas and the formed vapors; the fine material is fed into the cyclone suspension type heat exchanger system via a raw meal conveying device, while the separated gas (hot gas and vapors) is supplied for a dedusting via a fan.
The more coarse raw material portions that are still present after the drying process and that potentially have not yet dried up to the required residual moisture are downwardly transported in the step drier by means of gravitational force and are discharged through a discharge opening. For purposes of keeping an optimally low pressure loss in the step drier, the discharge opening is provided with a lock (such as an air lock), with a double rotary lock, for example. Subsequently, the step drier is fed via conveying devices (for example conveyor belts, bucket chain conveyor) with the coarse material, which is still moist and which is separated from the other material stream, together with fresh material.